<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=, initial-scale=1.0">
    <title>Document</title>
    <style>

       div{
        width: 200px;
        height: 200px;
        border:1px red solid;
        margin: 100px auto;
        /* 圆角边框 */
        border-radius: 0px 0px 0px 0px;
       }

    </style>
</head>
<body>

      <div>

      </div>
    
</body>
</html>